Method of deposition of non-conductive copper coatings from vapor phase



March 22, 1955 P PAWLYK 2,704,727

, METHOD OP DEPOSITION 0F NoN-CONDUCTIVE COPPER coATINGs FROM VAPOR PHASE Filed oct. s, 1951 2 sheets-sheet 1 INVENTOR PETER PAWLYK BY TMF/mk ATTORN EYS.

2 Sheets-Sheet 2 P. PAWLYK oooooo Hoooooojj PAWLYK ATTORNEYS lNvENToR PETER BYN METHOD OF DEPOSITION OF NON-CONDUCTIVE COPPER COATINGS FROM VAPOR PHASE March Z2, 1955 Filed oct. s, 1951 United States Patent VO METHOD F DEPOSITION OF NON-CONDUCTIVE COPPER COATINGS FROM VAPOR PHASE Peter Pawlyk, Dayton, Ohio, assignor to The Common- Wealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Application October 8, 1951, Serial No. 250,302

4 Claims. (Cl. 117-50) This invention relates to means and methods of obtaining uniform concentrations of mixed gases at constant temperatures. More particularly the invention relates to the control of gaseous mixtures, one of the gases of which is a metal-bearing compound decomposable under the influence of heat to deposit metal.

The efficient plating of objects with metals, by the pyrolysis of gaseous metal-bearing compounds and the deposition of the metallic component of the gas, requires close control of decomposition conditions in order that a ne uniform deposit may be obtained. Premature heating of the metal-bearing gas above the decomposition point induces uncontrolled decomposition in the gas plating apparatus, and thus deprives the process of emciency, since the concentration of metal in the gas striking the object to be plated will then be uncontrolled and in some cases insufficient to provide a uniform, adherent coat on the workpiece.

An inert carrier gas may be used together with the metal-bearing gas and serves as an effective diluent affording means of control of the concentration of the metal-bearing gas. Such inert gases are carbon dioxide, nitrogen, helium and argon.

This invention contemplates subjecting the metal-bearing compound in the liquid or solid state to the action of a carrier gas under controlled conditions of temperature, and effecting vaporzation of the metal bearing compound underthe controlled conditions to provide a plating gas mixture uniform in concentration and of predetermined temperature characteristics.

The invention also contemplates particular structural arrangements for the handling of the solid or liquid metal bearing compound, which arrangements facilitate the contact with the carrier gases to accomplish intimate contact between these primary components. Thus, for example, fusing together of the solid particles of metal bearing compound may be prevented by the arrangements of the invention.

The invention further contemplates the provision of novel procedural steps to assist in the attainment of the desired plating gas of uniform characteristics.

These and other allied purposes of the invention are attained by providing apparatus for the passage of the inert carrier gas through a pre-heating coil, maintained at a constant temperature, immediately prior to contacting the solid or liquid metal bearing component with the carrier gas, the metal bearing component itself being held at constant temperature conditions. The contact of the carrier gas with the metal-bearing component is facilitated by dispersing the particles of metal-bearing solid in a carburetor in layers, and interspersing glass beads or ceramic material with the metal-bearing solid to facilitate the dispersement. Glass wool and/or metal screening may be employed to support the metal-bearing solid compounds, and both are effective to cleanse the gases as well as to assist in contact thereof with the solid compound.

Where the metal-bearing compound is in the liquid state the inert carrier gases may be bubbled through the material, a procedure which is facilitated by the employment of horizontal screens spaced along the vertical axis of the carburetor. The screens are in this instance effective to. prevent the -entraining of the gas in restricted paths, and the minor turbulence created by the screen is sufficient to insure of adequate liquid contact by the gas.

In the process of invention the passage of the carrier gas under controlled conditions to the similarly con- 'Y trolled metal-bearing compound results in controlled temperature conditions in the gas mixture iiowing from the carburetor to the plating chamber. This gas mixture may be subjected to a further heating step before entering the plating chamber and such a step is particularly eifective where the desired gas temperature in the chamber is higher than the temperature which may be effectively employed in the carburetor.

The invention will be more fully understood by reference to the following detailed description and accompanying drawings wherein:

l Figure l is a schematic view of one embodiment of the invention;

Figure 2 is a longitudinal sectional view of the carburetor of the embodiment of Figure l;

Figure 3 illustrates a modification of the carburetor i system of Figure l;

Figure 4 illustrates another embodiment of the invention;

Figure 5 illustrates a method of packing the carburetor with solids; and

Figure 6 illustrates a modication of the structure of Figure 5.

Referring to Figure l there is shown at 10 a tank of liquiiied carbon dioxide provided with a valve 28 and from which extends a short copper conduit 9 having therein a gauge 36 which measures gas flow. The inner.

end of conduit 9 is formed into a coil 7 which surrounds the carburetor 4, the lower end of the coil being secured in the opening 5 (Figure 2) of the carburetor. The coil 7 and carburetor 4 are immersed in oil 3 contained in tank 2 and this assembl indicated generally at 1, is adapted to be maintained at an elevated temperature by electric heater element 29 secured beneath container 2. Heater element 29 may be provided with thermostatic means, including element 37 secured to the heater .by

conductor 3S, for automatically controlling the temperature of the oil 3 but where the volume of the oil is rela'-v tively large in comparison with the carburetor volume, and the temperature of the oil not greater than about 150 C. manual control is fully effective since electric heaters are readily obtainable which supply a substantially constant heat input.

At the upper opening 6 (Figure 2) of the carburetor 4 there is secured a conduit 12 which connects with plating chamber 24. Conduit 12 is provided with asbestos or other heat insulating material 33 and may in given instances be itself of a heat insulation material. Interposed between the carburetor d and the plating chamber, and surrounding conduit 12 is a heater 11.

The plating chamber 24 may be adapted to contain an object to be plated or may itself be the object which is to be plated. The latter arrangement is shown in Figure 1 wherein the internal walls of the chamber are to be coated with metal, and to eifect this the hollow tube or pipe member 24 is provided with end flanges 30, 31. Flange 30 secures the -member 24 to conduit 12 while ange 31 sccnres the chamber to an outlet line 32 provided with a vacuum pump 27 which exhausts to the atmosphere or a recovery apparatus as desired.

Chamber 24 is surrounded 25 surmounted by an electric heating coil 26 powered from a source (not shown).

In Figure 2 the carburetor 4 is shown provided with vertically arranged layers 13 of chromium carbonyl, supported on screens 15 which are separated by layers of glass wool 14. Metal screens 16 are positioned adjacent the inlet 5 and outlet 6 to provide a thoroughly dispersed gas ow. The metal screens 15 and 16, are approximately mesh and the powder particles thereon vary 'from about 2 to 5 times the size of the screen openings.

In the modification of Figure 3 the coil 7 and carburetor 4 are each immersed in oil 3 but the carburetor is not with a thinlayer of asbestos i immersed in the bath. Such an arrangement is particularly useful where the temperature variationv throughout i the bath is negligible and the arrangement is desirable due to the simplified mechanical connections. This structure is particularly useful in connection with liquid metal- Vtablishing good contact with the carrier gases.

bearing compounds as the carburetor may be readily recharged.

Figure 4 illustrates an embodiment of the inventlon m which the mixture of gases emanating from the carburetor 4 and heat jacket` 11, as in the embodiment of Figure-l, are passed through aY secondcoil 34, maintained in a constant temperature bath 18 containing oil V19 heated by element- 29. This arrangement is particularly suited for complete-stabilization of the temperature of the gases, the mixture emanating from this constant temperature bath then beingsubject to the heat of heating jacket 20 prior to entry to the plating chamber. This mode of raising the temperature in controlled steps is particularly eective Where the temperature of decomposition of themetal bearing gases is relatively high.

Figures 5 and 6 set forth arrangements of solid metalbearing compounds which are particularly suited for es- Numeral 21 of Figure 5 indicates glass beads interspersed with fragments 22 of s'olid chromium carbonyl. Numeral 23 in Figure 6 indicates beads of chromium carbonyl supported by screens 35.

In the operation of the apparatus the usual precautions are observed of providingV a clean workpiece and flushing of the apparatus free of air prior to entry of the plating gases. Referring particularly to Figure l, carbon dioxide gas is bled from cylinder 10Ainto coil 7 through end 9 and attains a temperature substantially equal to that of the oil bath'before entering the carbureting chamber 4 at 5. The carburetor is, as noted, packed with chromium carbonyl fragments which also are at substantially the temperature of the oil bath,'in the present case 170 C. Preferably the temperature of the oil bath and gases entering the carburetor is between about l to 40 C. higher than that required for vaporization of the carbonyl. Thus the slight tendency of the gases to cool as they expand into the carburetor is not a serious factor in the operation of the equipment.

It will be clear that the particular temperature of the enteringV gases is a variable factor depending uponthe physical dimensions of the carburetor and coil, the method of packing theV carburetor and the particular compound to be volatilized. However, it Will not generally be necessary to raise the temperature of the incoming gases more than 40 C. above that required for vaporization of the carbonyl.

Y The hot carrier gas contacting the carbonyl vaporizes the same and the mixture of gases flows upwardly, under the inuence of the pressure of the carrier gas, to the heating jacket 11, where additional heat is supplied to the gases, the temperature of which however is still below the decomposition point of the chromium carbonyl.

The packing of the carburetor in the indicated manner tends to eliminate any tendency of the metal bearing com- Y pounds to fuse together and consequently uniform gas flow to the plating chamber is assured with the apparatus of invention.

The metal-bearing gas entering the plating chamber 24, at flow rates of the carbon dioxide measured at the tank 10 of between about yl liter to 8 liters per minute, will fill the chamber uniformly with plating gas which decomposes under the iniinence of the heat of the chamber depositing chromium on the interior walls of the chamber.

'The pressure of the gases in the'chamber may be maintained by the vacuum pump 27 at a pressure of 5 to 7 pounds absolute, although this pressure may be varied upwardly to speed the plating time, or lowered to achieve deposits of very ne metal. The temperature of the chamber wall in the present instance is about 600 F. and may be varied between about S50-700 F. to change the rate of deposition of metal. However, under the conditions noted, and a pressure of -7` pounds, a uniform `plating having a thickness of approximately .003 may be obtained in about 50 to 60 minutes over the interior length of a 5" tube. v Y

The attainment of a uniform mixture of carrier and metal-bearing gas at the entrance to the plating chamber isi essential to the uniform deposition of the metal and leads to the result noted above. Where the temperature of the carburetor is-considerably below that desiredfor optimum plating of: the workpiece, the uniformgas mixture emanating from the carburetor may; be additionally heated with the apparatus of- Figure 4 whilefmaintanng uniformity inthe gas mix.

The feature of pre-heating above'the vaporization point However, in instancesV of the metal-bearing compound insures of maximum and uniform vaporization at a given internal temperature of the carburetor. Where the carburetor and coil are exposed to the same oil bath a vapor pressure of carbonyl will of course exist over the fragments but the physical arrangement of the system is such that little carbonyl will ow until the carrier gas sweeps away the carbonyl allowing more of the material to vaporize.

All metal-bearing gases ywhich are subject to decomposition by heat to result in the deposition of the metallic component may be suitably employed in the process and apparatus of invention. Thus the solid metal-bearing compounds such as molybdenum carbonyl, tungsten carbonyl, and cobalt carbonyl, as Well as liquids, for example, the nickel carbonyl and iron penta carbonyl, may be employed. The hydrides lof antimony and tin, chromyl chloride, copper nitroxyll and cobalt nitrosyl carbonyl are other effective agents.

This application is related to copending applications, Serial Nos. 250,301; 250,303; 250,304; 250,305; 250,306; and 250,307; all liled October 8, 1951-, and all by the same inventor as the present application.

It will be understood that this invention is susceptible to modification in order to adapt it to diiferent usages and conditions and accordingly, it isy desired to comprehend such modications within this invention as Vmay fall within thescope of the appended claims.

I claim:

l. The method of gas plating on an object which method comprises: heating an object to a decomposition temperature for metal bearingI vapors in a plating zone, heating a thermally decomposable metal-bearing compound in a substantially enclosed spacing to a temperature suficient to produce vapors of the compound and insuicientto effect decomposition of theV compound, separately heating a carrier gas to a temperature which is substantially that of thecompound and its vapors and then owing the heated carrier gas into contact with said heated metal-bearing compound and vapors in the spacing to produce a heated mixture of carrier-gas borne metal bearing vapors, and owing the resultant mixture and insufficient to effect -thermal decomposition of the compound, separately heating a carrier gas to a temperature which is substantiallv that of the solid compound and the vapors and flowing Athe heated carrier gas into contact with said solid compound and said enclosed spacing to produce a heated mixture of carrier-gas borne metal bearing vapors, and flowing the resultant mixture of gases to the plating zone into contact with the heated object to be plated.

3. The method of gas plating on an obiect which method comprises: heating an object to a decomposition temperature for metal bearing vapors in a plating zone, packing a substantially enclosed ,spacing with fragments of a solid metal bearing compound the vapors of which are thermally decomposable, heating the compound in the substantially enclosed spacing to a temperature sufficient to produce vapors of the compound and insuflicient to eiect thermal decomposition of the compound, separately heating a carrier gas to a temperature which is substantially that of the solid compound and the vapors and flowing the heated carrier gas into contact with said solid compound and said enclosed spacing to produce a heated mixture of carrier-gas borne metal bearing vapors, heating the resultant mixture of gases above the temperature in the spacing'but below the temperature of the heated object, and thereafter passing the heated mixture of gases to the plating zone into contact with the object. to be plated.

4. The method of gas plating on an object which method comprises: heating an object in a plating zone to a temperature above the thermal decomposition point of chromiumv carbonyl, heating chromium carbonyl in a vconfined spacing to a temperature of about C. to

produce vapors of chromium carbonyl, separately heatthen owing the heated carbon dioxide into contact with said carbonyl compound and vapors of the carbonyl to produce a heated mixture of chromium carbonyl and carbon dioxide, and then owing the resultant mixture of gases to the plating zone and into contact with the object to be plated.

References Cited in the fdc of this patent UNITED STATES PATENTS 974,812 Parker Nov. 8, 1910 1,136,675 Hutchinson Apr. 20, 1915 1,794,810 Van Arkel et al. Mar. 3, 1931 6 Bacon Aug. 18, 1936 Holler Mar. 28, 1939 Swinburne Oct. 26, 1940 Germany Mar. 17, 1942 Christensen June 2, 1942 Lang Dec. 8, 1942 Drummond Oct. 19, 1943 Drummond Mar. 14, 1944 Fink Nov. 27, 1951 FOREIGN PATENTS Great Britain Sept. 22, 1936 

1. THE METHOD OF GAS PLANTING ON AN OBJECT WHICH METHOD COMPRISES: HEATING AN OBJECT TO A DECOMPOSITION TEMPERATURE FOR METAL BEARING VAPORS IN A PLANTING ZONE, HEATING A THERMALLY DECOMPOSABLE METAL-BEARING COMPOUND IN A SUBSTANTIALLY ENCLOSED SPACING TO A TEMPERATURE SUFFICIENT TO PRODUCE VAPORS OF THE COMPOUND AND INSUFFICIENT TO EFFECT DECOMPOSITION OF THE COMPOUND, SEPARATELY HEATING A CARRIER GAS TO A TEMPERATURE WHICH IS SUBSTANTIALLY THAT OF THE COMPOUND AND ITS VAPORS AND THEN FLOWING THE HEATED CARRIER GAS INTO CONTACT WITH SAID HEATED METAL-BEARING COMPOUND AND VAPORS IN THE SPACING TO PRODUCE A HEATING MIXTUIRE OF CARRIER-GAS BORNE METAL BEARING VAPORS, AND FLOWING THE RESULTANT MIXTURE OF GASES TO THE PLATING ZONE INTO CONTACT WITH THE HEATED OBJECT TO BE PLATED. 